(this post has been updated here)
You can collaborate with other musicians online using file sharing applications and digital audio workstations. In some DAW's all song data is embedded in the project file (audio tracks, midi tracks, and tempo information). There are things to consider when collaborating with multiple DAW’s.
If possible choose a single DAW to work with and use only stock plugins. This way you can use a single song folder/file when adding your parts. I typically keep a backup file on my computer and create folders for each person on a shared drive. To add your parts just copy the latest file/folder to your computer and add your tracks. Once completed the song can be uploaded back to your shared folder.
Splice even offers a free service to back up your work in the cloud and collaborate with other artists. https://splice.com/features/studio
Render or freeze any virtual instruments as audio if the person receiving the files does not own the plugin.
Export all audio files as separate tracks, and if necessary include the empty sections from start to finish, so the tracks line up in the sequencer when imported.
Select the correct tempo before importing the tracks.
Provide the songs key.
I typically share documents and pictures that explain details of the recording like song key, song arrangement, and music equipment used for each track.
Online collaboration is great when musicians live far away from each other. It can also be used as a practice tool so everyone in the band can figure out their individual parts before a practice.
Just don't forget to go over other important details like availability and scheduling conflicts. If the project is successful then you will need to talk about payment splitting, distribution, and copyright.
Online Collaboration resources